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United States Patent |
6,050,233
|
Vilou
|
April 18, 2000
|
Controller for a vehicle starter motor
Abstract
A controller for a vehicle starter motor, the controller comprising means
for applying power to the electric starter motor as a function in
particular of the open or closed state of a starter switch, wherein said
means include in particular an RC type circuit having a charging time
constant that is shorter than its discharging time constant and that
charges and discharges depending on whether the starter switch is closed
or open, said control means also including means for preventing power
being applied to the starter motor when the voltage across the terminals
of the capacitor means of the RC circuit exceeds a given threshold.
Inventors:
|
Vilou; Gerard (Tassin, FR)
|
Assignee:
|
Valeo Equipments Electriques Moteur (Creteil, FR)
|
Appl. No.:
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177351 |
Filed:
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October 23, 1998 |
Foreign Application Priority Data
Current U.S. Class: |
123/179.3; 290/38R |
Intern'l Class: |
F02N 011/08 |
Field of Search: |
123/179.3
290/38 R
|
References Cited
U.S. Patent Documents
3594029 | Jul., 1971 | Holt | 290/38.
|
4104534 | Aug., 1978 | Hill et al. | 123/179.
|
4883028 | Nov., 1989 | Wu | 123/179.
|
4901690 | Feb., 1990 | Cummins et al. | 123/179.
|
5094199 | Mar., 1992 | Griffin | 123/179.
|
Foreign Patent Documents |
0 526 307 | Feb., 1993 | EP.
| |
32 33 596 | Mar., 1984 | DE.
| |
41 06 247 | Apr., 1992 | DE.
| |
93 19 621 U | Mar., 1994 | DE.
| |
43 38 638 | Jun., 1994 | DE.
| |
2 239 569 | Jul., 1991 | GB.
| |
Primary Examiner: Dolinar; Andrew M.
Attorney, Agent or Firm: Morgan & Finnegan, LLP
Claims
I claim:
1. A controller for a vehicle starter motor, the controller comprising
means for applying power to the electric starter motor as a function in
particular of the open or closed state of a starter switch, wherein said
means include in particular an RC type circuit having a charging time
constant that is shorter than its discharging time constant and that
charges and discharges depending on whether the starter switch is closed
or open, said control means also including means for preventing power
being applied to the starter motor when the voltage across the terminals
of the capacitor means of the RC circuit exceeds a given threshold, and
wherein the RC circuit is constituted by two parallel-connected branches,
one comprising a series connection of first resistor means and the
capacitor means, the other comprising second resistor means.
2. A controller according to claim 1, wherein the resistor means in series
with the capacitor means of the RC circuit are of resistance that varies
as a function of temperature.
3. A controller for a vehicle starter motor, the controller comprising
means for applying power to the electric starter motor as a function in
particular of the open or closed state of a starter switch, wherein said
means include in particular an RC type circuit having a charging time
constant that is shorter than its discharging time constant and that
charges and discharges depending on whether the starter switch is closed
or open, said control means also including means for preventing power
being applied to the starter motor when the voltage across the terminals
of the capacitor means of the RC circuit exceeds a given threshold, and
wherein the control means comprise a microprocessor which controls the
application of power to the electric starter motor as a function in
particular of the closed or open state of the starter switch, and wherein
the RC circuit is fed with voltage via an output of said microprocessor.
4. A controller for a vehicle starter motor, the controller comprising
means for applying power to the electric starter motor as a function in
particular of the open or closed state of a starter switch, wherein said
means include in particular an RC type circuit having a charging time
constant that is shorter than its discharging time constant and that
charges and discharges depending on whether the starter switch is closed
or open, said control means also including means for preventing power
being applied to the starter motor when the voltage across the terminals
of the capacitor means of the RC circuit exceeds a given threshold, and
wherein the control means comprise a microprocessor controlling the supply
of power to the electric starter motor as a function in particular of the
closed or open state of the starter switch, and wherein a voltage
corresponding to the voltage across the terminals of the capacitor means
of the RC circuit is injected into an input of said microprocessor, said
microprocessor causing the supply of power to the starter motor to be
blocked when said voltage exceeds a given threshold.
5. A controller for a vehicle starter motor, the controller comprising
means for applying power to the electric starter motor as a function in
particular of the open or closed state of a starter switch, wherein said
means include in particular an RC type circuit having a charging time
constant that is shorter than its discharging time constant and that
charges and discharges depending on whether the starter switch is closed
or open, said control means also including means for preventing power
being applied to the starter motor when the voltage across the terminals
of the capacitor means of the RC circuit exceeds a given threshold, and
wherein the ratio between the charging time constant and the discharging
time constant is substantially equal to the ratio between the heating time
constant and the cooling time constant of the starter motor.
6. A controller for a vehicle starter motor, the controller comprising
means for applying power to the electric starter motor as a function in
particular of the open or closed state of a starter switch, wherein said
means include in particular an RC type circuit having a charging time
constant that is shorter than its discharging time constant and that
charges and discharges depending on whether the starter switch is closed
or open, said control means also including means for preventing power
being applied to the starter motor when the voltage across the terminals
of the capacitor means of the RC circuit exceeds a given threshold, and
wherein the means which prevent power being applied to the starter motor
when the voltage across the terminals of the capacitor means of the RC
circuit exceeds a given threshold prevent power being reapplied to the
starter motor until said voltage has dropped below a second threshold
lower than the first.
7. A controller for a vehicle starter motor, the controller comprising
means for applying power to the electric starter motor as a function in
particular of the open or closed state of a starter switch, wherein said
means include in particular an RC type circuit having a charging time
constant that is shorter than its discharging time constant and that
charges and discharges depending on whether the starter switch is closed
or open, said control means also including means for preventing power
being applied to the starter motor when the voltage across the terminals
of the capacitor means of the RC circuit exceeds a given threshold, and
wherein the voltage threshold above which the supply of power to the
starter motor is prevented varies as a function of one or more operating
parameters of the starter motor and/or of the engine.
8. A controller for a vehicle starter motor, the controller comprising:
a microprocessor for monitoring the level of heat of a starter motor
comprising means for determining whether a starter switch is open or
closed, the microprocessor outputs a supply voltage when the starter
switch is closed;
a first circuit having a capacitor for receiving the supply voltage, the
first circuit having a charging time constant that is shorter than its
discharging time constant, and the first circuit charges and discharges
according to the supply voltage;
a second circuit for controlling a power supply source to the starter
motor, the second circuit being operatively connected to the
microprocessor and being controlled by the microprocessor to prevent power
to be applied to a starter motor when the temperature of the starter motor
exceeds a threshold temperature.
9. The device according to claim 8 wherein the first circuit is an RC-type
circuit.
10. The device according to claim 9 wherein the ratio between the charging
and discharging time constants is substantially equal to the ratio between
a heating time constant and a cooling time constant of the starter motor.
11. The device according to claim 10 wherein the microprocessor monitors
the temperature of the starter motor by measuring the voltage across the
capacitor.
12. The device according to claim 11 wherein the capacitor has a
predetermined threshold voltage wherein the amount of time for the
capacitor to reach the threshold voltage corresponds to the amount of time
the starter motor requires to reach a maximum limit temperature.
13. The device according to claim 12 wherein the microprocessor controls
the second circuit to prevent power from being applied to the starter
motor when the voltage across the capacitor exceeds the threshold voltage.
14. The device according to claim 13 wherein a resistance of a resistor of
the RC-type circuit varies as a function of the temperature of the starter
motor.
Description
The present invention relates to controllers for vehicle starter motors.
BACKGROUND OF THE INVENTION
Controllers for controlling a starter motor electronically are now
conventional. They generally include a control unit which receives as an
input a flag concerning the open or closed state of a starter
switch--which switch is generally actuated by the vehicle key--and which
controls the application of power to the coil(s) of a power contactor
which, when closed, serves to power the electric starter motor. The power
contactor includes, in particular, a moving core which, at the end of its
stroke, closes the power supply circuit for the electric starter motor and
whose displacement causes the starter pinion to be entrained towards the
ring gear. This control unit also serves to control other functions such
as automatically stopping the starter or indeed providing protection
against surge currents or against operator error such as trying to start
an engine that is already running. The control unit is either integrated
within the starter itself, or else it is housed externally thereto in a
special box. In another variant it may be constituted by an
already-existing electronic system, such as the injection and ignition
processor.
It can happen, particularly in the event of some kind of vehicle breakdown,
that the user makes numerous successive attempts at operating the starter
motor in the hope of starting the engine.
Each time it is activated, the starter motor heats up quickly and its
temperature rises significantly--by a few degrees--as a function of its
operating characteristics and as a function of the length of time it is
activated. The lengths of the pauses between successive attempts at
starting are of the order of a few seconds and they enable the starter
motor to cool down to some extent. However, its rate of cooling is much
slower than its rate of heating, such that as a general rule the starter
motor is far from returning to its initial temperature when it is
reactivated.
This gives rise to a cumulative heating effect which, if too many attempts
are made or if they last for too long, will lead to the starter motor
being destroyed.
Unfortunately, it turns out to be impossible to protect the starter motor
against being destroyed in that way merely by requiring sufficiently
lengthy pauses between two successive closures of the power contactor: the
control unit, which is generally constituted by a microprocessor, loses
power between two successive actuations of the contact switch, and that
makes it impossible to use the internal clock of said control unit for
measuring time.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the invention is therefore to provide a controller for
electronically controlling a vehicle starter motor in such a manner as to
protect it against damage, in particular thermal damage, of the kind that
can arise if the starter motor is actuated too many times in succession.
To this end, the invention provides a controller for a vehicle starter
motor, the controller comprising means for applying power to the electric
starter motor as a function in particular of the open or closed state of a
starter switch, wherein said means include in particular an RC type
circuit having a charging time constant that is shorter than its
discharging time constant and that charges and discharges depending on
whether the starter switch is closed or open, said control means also
including means for preventing power being applied to the starter motor
when the voltage across the terminals of the capacitor means of the RC
circuit exceeds a given threshold.
The controller advantageously further exhibits the following
characteristics taken singly or in any technically feasible combination:
the RC circuit is constituted by two parallel-connected branches, one
comprising a series connection of first resistor means and the capacitor
means, the other comprising second resistor means;
the control means comprise a microprocessor which controls the application
of power to the electric starter motor as a function in particular of the
closed or open state of the starter switch, and the RC circuit is fed with
voltage via an output of said microprocessor;
the RC circuit is connected to a voltage supply terminal via the starter
switch, optionally in series with a voltage regulator circuit;
the control means comprise a microprocessor controlling the supply of power
to the electric starter motor as a function in particular of the closed or
open state of the starter switch, and a voltage corresponding to the
voltage across the terminals of the capacitor means of the RC circuit is
injected into an input of said microprocessor, said microprocessor causing
the supply of power to the starter motor to be blocked when said voltage
exceeds a given threshold;
the means which prevent power being applied to the starter motor when the
voltage across the terminals of the capacitor means of the RC circuit
exceeds a given threshold include an analog threshold comparator circuit;
the ratio between the charging time constant and the discharging time
constant is substantially equal to the ratio between the heating time
constant and the cooling time constant of the starter motor;
the means which prevent power being applied to the starter motor when the
voltage across the terminals of the capacitor means of the RC circuit
exceeds a given threshold prevent power being reapplied to the starter
motor until said voltage has dropped below a second threshold lower than
the first;
the voltage threshold above which the supply of power to the starter motor
is prevented varies as a function of one or more operating parameters of
the starter motor and/or of the engine; and
the resistor means in series with the capacitor means of the RC circuit are
of resistance that varies as a function of temperature.
BRIEF DESCRIPTION OF THE DRAWING
Other characteristics and advantages of the invention appear further from
the following description. The description is purely illustrative and
non-limiting. It should be read with reference to the accompanying
drawing, in which:
FIG. 1 shows a controller constituting one possible embodiment of the
invention; and
FIGS. 2a to 2c show an operating sequence for the FIG. 1 controller.
MORE DETAILED DESCRIPTION
FIG. 1 shows the electric starter motor M of a vehicle, together with the
power contactor 1 which controls the supply of power to the motor M.
The starter motor M is connected between ground and a terminal B+ that is
at the power supply voltage of the battery.
The power contactor is constituted by a relay having driving and holding
coils 1b and 1c and a contact 1a which is interposed between the power
supply terminal B+ and the starter motor M.
An end common to both coils 1b and 1c is connected to the B+ terminal by
means of a controlled switch (transistor T) in series with a vehicle
starter switch (switch 2, e.g. as actuated by the vehicle key).
The driving coil 1b is connected between said common end and a point
between the contact 1a and the motor M.
The holding coil 1c is mounted between said common end and ground.
By way of example, the switch T can be a transistor of the MOSFET type.
It is controlled by a control unit 3 which is a microprocessor that
generates a control voltage on the grid of said transistor T so as to
control the sequence with which power is applied to the coils 1b and 1c as
a function both of the various stages of operation of the starter (power
to drive the contact, power to hold the contact closed, automatically
stopping the starter after the engine has started, etc.) and also as a
function of the various protective actions that the microprocessor 3 can
control (protection against starting again once the engine is running, for
example).
To generate the control voltage, the control unit 3 takes into account in
particular the open or closed state of the switch 2. To this end, said
unit 2 has an analog input "e0" having injected thereon the voltage of a
point between the starter switch 2 and the controlled switch T.
Also, in accordance with the invention, the controller shown in FIG. 1 has
means 4 that prevent the motor M being actuated on successive occasions
that are too close together.
The means 4 comprise, in particular, an RC type circuit having a charging
time constant that is smaller than its discharging time constant and which
charges or discharges depending on whether the switch 2 is closed or open.
The means 4 also have means enabling power supply to the motor M to be
prevented whenever the voltage across the terminals of the capacitor C is
greater than a given threshold (which means that the capacitor has not
discharged sufficiently from the most recent occasion(s) on which the
starter switch was closed).
In the example shown in FIG. 1, the RC circuit is constituted by two
branches connected in parallel, one comprising a resistor R1 in series
with the capacitor C, and the other comprising a single resistor R2.
These two branches are connected between ground and an analog output "s1"
of the microprocessor 3, which output supplies voltage to said branches
when the switches 2 and T are closed.
A diode D which conducts from said output s1 to ground is interposed
between said output s1 and said branches R1-C and R2.
The voltage across the terminals of the capacitor is injected via an analog
input "e1" to the microprocessor 3 and the microprocessor causes the
switch T to be switched off whenever the key-operated switch 2 is closed
while said voltage is greater than a given threshold. It causes the switch
T to close only once said voltage has dropped below said threshold.
The circuit operates as follows.
When the switch 2 is closed, the microprocessor 3 is powered.
Its output "s1" enables the capacitor C to be charged via the resistor R1
throughout the time that power is applied to the starter motor M.
When the switch 2 is opened, the microprocessor 3 is no longer powered, so
the capacitor C stops being charged.
It then discharges via the resistors R1 and R2 in series.
Because of the presence of the resistor R2 in the discharge circuit, the
time constant for discharging the capacitor is longer than the time
constant for charging it.
The ratio between the charging and discharging time constants is preferably
chosen to be substantially equal to the ratio between the heating and
cooling time constants of the starter motor, thus making it possible at
any instant to have a good representation of the state of starter motor
heating by measuring the voltage across the terminals of the capacitor.
This voltage is continuously monitored by the microprocessor via its analog
input "e1".
Variations in the voltage across the capacitor C as a function of time are
shown by way of example in FIG. 2a.
Each time the switch 2 is closed (FIG. 2b shows the opening and closing
sequence), the capacitor C charges while the starter motor is in
operation. Discharging takes place when the switch 2 is open, i.e. while
the starter motor is stopped.
If starts are close enough together, the voltage across the terminals of
the capacitor C rises progressively as does the temperature of the starter
motor.
Once the voltage exceeds a predetermined threshold corresponding to a
temperature state that is below a maximum limit temperature, the
microprocessor 3 turns off the contactor-controlling transistor, thereby
preventing power being applied to the starter motor and thus avoiding any
irreversible damage thereto due to overheating. This is shown in FIG. 2c
where there can be seen a sequence of commands applied to the contactor 1.
A new attempt at starting can take place only after the voltage has dropped
back below the cutoff threshold by an amount lying in the range 0 to 100%
of the threshold.
Variant embodiments other than that described above are naturally possible.
In particular, instead of being powered by the microprocessor 3, the RC
circuit may be powered by the vehicle key, e.g. via a voltage regulator
circuit.
Also, instead of injecting the voltage across the terminals of the
capacitor C into the microprocessor 3, it is possible to provide for the
capacitor C to be connected across the terminals of an analog circuit
which includes a threshold comparator, optionally together with an input
amplifier, said circuit then switching off the transistor T whenever the
voltage injected to the said comparator exceeds said threshold.
In another variant, the voltage threshold below which the starter motor M
is prevented from operating can vary as a function of one or more
parameters, in particular as a function of the temperature of the starter
motor, of the temperature of the engine, of the electric current drawn
while starting, of the speed at which the engine is driven, of the
frequency of ripple in battery voltage or current due to the engine
passing through its compression points, or indeed of any other information
from which it is possible to make a deduction concerning the extent to
which the starter motor is overheating.
In addition, the charging resistance of the capacitor may include elements
that vary as a function of ambient temperature such as a negative
temperature coefficient (NTC) resistor.
Also, the capacitor C can be charged using a chopped voltage or a string of
pulses having a duty ratio that is variable so as to modulate charging
continuously as a function of the heating characteristics that appear
during starting.
As will be understood, a controller of the type described above is a simple
controller that provides thermal protection for an electric starter motor
without requiring temperature sensors to be placed in critical zones of
the motor and without requiring connections between such sensors and the
circuit board on which the starter motor controller is mounted.
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